Condensation vacuum pump



I "in order for the jet to the Jet towards sure against whi vide a baliie between Patented July 15 1941 CONDENSATION VACUUM PUMP Frank Edmund Walter Miller, R signors, by

Bancroft, Sale, and Charles undhay, Leeds, England, asmesne assignments, to General Electric Company, a corporation of New York 1940, Serial No. 322,936

Application March 8,

- 'In Great Brita in March 18, 1939 -3 Claims. (cl. 230-101)- This invention relates to condensation or' diffusion vacuum pumps of the kind designed and constructed for operation with an organic liquid,.i"or example the oil which is known as Apiezon" oil (Apiezon being a registered trade: mark), or other organic liquids having a vapour pressure considerably lower than that of mercury.

The invention improvements in has for its object to provide such pumps whereby to improve the backing pressure characteristic or, inother words, the

fore-vacuum pressure against which the pump may be capable of operating.

In considering such pumps it is known that, to be capable of operating against a high fore-vacuum pressure, the density of the vapour in the space immediately next the fore-vacuum side of the pump should be as high as possible. However, the total number of vapour molecules issuing from the jet is obviously limited by such factors as the temperature and superficial area of the boiler, and the vapourpressure 'oi' the pump filling at the temperature of the boiler. also known that increase of the boiler temperature and of the vapour pressure of the pump filling causes an increase in the maximum forevacuum pressure against which the jet will operate. -Moreover, in the case of multi-stage pumps,such factors as the vapour pressure of the filling and the boiler temperature are restricted by considerations of the ultimate vacuum pressure which it is desired should be obtained with the jet nearest the high-vacuum end or part of the pump.

It is-thus apparent that the backing pressure characteristic of any given pump can be improved only to a limited extent by variation of the pump filling and boiler temperature. Moreover, even when these factors have been seiected at their optimum value it is desirable that further increase in the fore-vacuum presh the pump will operate should be t ine ii."

With t e ;-aboye and other considerations in view it is proposed according to the present invention, in a pump pf the kind specified to prothe hot vapour uptake pipe or duct and the condenser surface so as to constrict the space into which is fed the I specification of British Patent No. 346,293, the form -of a depending skirt 9 ter adjacent the jet jet and the fore-vacuum outlet. With such provision, since the total number of vapour molecules issuing from the jetis to a first approximation fixed by the factors aforementioned, the density of such increased and thus the backing pressure characteristic of the pump improved. Other advantages will hereinafter appear.

Conveniently, in the case of a vertical tubular pump the bafile referred to may be in the form of a thin-walled skirt surrounding and spaced from the uptake pipe and attached to the latand extending from the latter beyond the fore-vacuum outlet.

,Thus, for example, in applyingthe invention to pumps of the construction disclosed in the baflie may be in the I surrounding the uptake pipe wholly across the molecules in the space will be mouth of the fore-vacuum pipe;- being arranged to extend from a point on the uptake pipe adjacent the cowl to a point appreciably below the mouth of the fore-vacuum pipe; with this provision the baflies which were secured to the uptake pipe in the aforesaid specification so as to extend to within a short distance from the pump body below the fore-vacuum pipe may be omitted. r

In applying the invention to amulti-jet pump having a single uptake pipe or a plurality of respective uptake pipes such as disclosed in the specification of U. S. application Serial No. 313,390, filed January 11, ,1940,.the baflle may be in the form of a skirt surrounding the uptake pipe or the outer uptake pipe and extendthe necessity for the provision of other ballles vapour from' thejet to the fore-vacuum pipe or outlet, or, in other words, between the jet and the fore-vacuum pipe or outlet in the case of a single stage pump or, in the case of a multistage pump, between the high backing pressure secured to the lower end of the uptake pipe' for this purpose. I

By the use of a thin-walled ballie it will be appreciated that it" .will

and that of the condensing surface; it will therefore be acting in some measure as a shield conservingheat in the uptake pipe, whilst in the small distance from.

tore-vacuum outlet.

assume a temperature intermediate between that of theuptake pipe region of the fore-vacuum pipe or aperture the battle will assist in the condensation of the vapour travelling down from the jet through the vapour reception space. 1

To enable the invention to be more fully understood twoarrangements thereof will now be described by way of example with reference to Figs. 1 and 2 of the accompanying drawing, showing in sectional elevation two arrangements of pump to which the invention is applied, like reference numerals being used in both figures where applicable.

In the accompanying drawing at, l is shown the boiler space for the organic liquid and at 2 an enclosure for an electric or other heater for the boiler I.

At 3 in Fig. 1 is shown a single vapour uptake pipe supplying at its upper end (not shown) a high vacuum jet which may be generally similar to the high vacuum jet 4 shown in Fig. 2.

In Fig. 1 at 5 is shown a cowl providing a jet 6 which is in tandem with'the upper jet (not shown) and which is supplied with vapour through perforations I in the common uptake tube 3.

At 8 is shown the condenser surface, cooled by the circulation .of fluid in the jacket 9.- At I0 is shown the fore-vacuum pipe which is connected to the main pump body or casing at a place beneath'the jacket 9.

In the arrangement-shown in Fig. 2 there are two uptake pipes 3 and 3arespectively for the upper jet 4 and the lower jet 8. At H in Fig. 2 is shown a sleeve or liner which per se forms the subject matter of aforesaid U. S. application Serial No. 313,390.-

In accordance with the present invention'the vapour receptionspace beneath the lower jet 6, in either of the illustrated. arrangements, is restricted by means of the baffle skirt I! which, as will be seen extends from the region of the jet 6 in the form of a cylindrical tube spaced away as at l3 from the uptake tube 3 and extendcation Serial No. 313,390. In such a pump, in

the absence of the baffle skirt l2, the lower jet 6 was capable of operating against a fore-vacuum pressure of approximately 340,1. when using a pump filling of being wattage of 600. When the baffle skirt I! was added the pump was capable of'operating against a backing pressure up to 420 or more.

With the arrangement shown in Fig. 2 it has also been found that the speed of the jet 6 can the upper end of the sleeve or liner H the part thereof indicated by the dotted lines l6 so that the flaring at the upper end of said sleeve or liner is as shown in full lines.

We claim:

1. A diffusion Dump providing internal condensing surfaces, a vapor source within the casing, a vapor duct leading upwardly from the said source, a pumping jet supplied with vapor from the said duct and so directed that the discharged vapors are projected downwardly against the condensing surfaces of the pump casing, a fore-vacuum pipe communicating with the interior of the pump casing at a point materially below the said jet and a bafiie surrounding the said vapor duct and extending generally parallel thereto for a substantial poring downwards beyond the mouth of the forevacuum pipe Ill. Preferably the lower end of the baflie skirt I2 is outwardly flared as shown at H, for the purpose hereinbefore indicated.

The bailie skirt I2 is preferably supported and centred in position by means of spacing pins l5 extending through holes in the baffle and bearing at'their inner ends on the uptake pipe 3 and bearing at their outer ends against the condenser surface 8. Preferably the battle skirt and the pins 15 or any other means for supporting it from the uptake pipe 3 are constructed of a material having .a relatively low thermal conductivity as for example mild steel or copper-nickel allov so that said baiile skirt and supporting means are in general maintained-at a temperature below that of the uptake pipe. I g The invention hasbeen found in practice particularly advantageous inthe high speed multistage pump illustrated in Fig. '2 and' described in the speciflcatioh of the aforesaidU. S. appli- ,tion of .its length, the spacingbetween the said battle and the said condensing surfaces being less than about half the spacing between the condensing surfaces and the vapor duct, whereby the passage between the vapor jet and the forevacuum pipe is materially restricted by the presence of the bafiie.

2. A diffusion pump comprising a pump casing providing internal condensing surfaces, a vapor source within the casing, a vapor duct leading upwardly from the said source, a pumping jet supplied with vapor from the said duct and directed downwardly in such fashion that the discharged vapors are projected against the condensing surfaces of the-pump casing, a forevacuum pipe connecting with the interior of the pump casing at a point materially below the said jet, and a baflle surrounding the said vapor duct in a region extending from the vapor jet to a point below the said point of connection of the fore-vacuum pipe, the spacing between the said baffle and the said condensing surfaces being less than about half the spacing between the condensing surfaces and the vapor duct, whereby the passage between the vapor jet and the said pipe is materially restricted by the presence of the baflie.

3. A diffusion pump according to claim 2 wherein the end of the baiile which extends below the point of connection of the fore-vacuum pipe is flared outwardly so as to extend close to the wall of the pump casing.

FRANKEDMUTND BANCROFT. CHARLES WALTER MILLER.

a registered trade-mark) and with a heater including a pump casing 

